1. Field of the Invention
This invention relates to a magnetic recording and reproducing device using a double-layered magnetic recording medium comprising a first magnetic recording layer for magnetic recording which has anisotropy perpendicular to the medium plane and a second magnetic layer having a lower coercive force than that of the first magnetic recording layer; information is recorded by magnetizing the recording medium in a direction perpendicular to the recording medium plane. The recording is effected by using a single pole magnetic head and the information is reproduced by using a ring type magnetic head.
2. Description of Prior Art
In currently used magnetic recording and reproducing devices for computer systems, (for example: magnetic disk units, magnetic tape units, magnetic drum units, and flexible disk units), magnetic materials are formed on a solid or flexible non-magnetic substrate by coating or electroposition techniques. These magnetic materials are used as the recording medium and data recording and reproducing can be effected by using a ring type magnetic head. In such a magnetic recording and reproducing device, magnetization of the recording medium in the direction of movement, (defined as the longitudinal direction), is employed. However, such a recording system, (hereinafter referred to as a longitudinally magnetized recording system), has the following disadvantage. Namely, when the recording density is increased, the demagnetization field in the medium increases and such an increase in the demagnetizing field causes the attenuation and the rotation of the residual magnetization resulting in a reduction of the output amplitude during reproduction.
Therefore, various improvements have been proposed in order to realize a higher recording density using conventional longitudinally magnetized recording systems. In order to reduce the aforementioned demagnetization in longitudinally magnetized recording systems, the saturation magnetization of the magnetic recording layers must be reduced and the magnetic recording layers must be made thinner. In addition, the coercive force of the magnetic recording layers must be increased. Furthermore, the saturation magnetization density of the core material of the recording head core must be made larger so as to sufficiently magnetize the recording layers. Furthermore, in order to increase the amplitude of the reproducing output and improve the output resolution, the spacing between the recording medium and the magnetic heads, (i.e.-the head floating height), and the reproduction gap length must be made as small as possible.
In order to improve the aforementioned conditions, efforts have been made to fabricate a thin magnetic material having a high coercive force for use as the recording medium layer. However, various difficulties have been encountered, such as the difficultly in producing a homogeneous magnetic thin film having high yields and the difficulty of producing a magnetic material having the proper magnetic characteristic so as to enable the generation of a signal sufficient for reproduction when said material is applied in a very thin layer.
High density recording techniques furthermore result in the following problems with respect to the recording and reproducing heads. The floating stability in a recording system having a small head floating height must necessarily be high and the floating stability is largly dependant on the mechanical characteristics of the system such as the surface roughness of the magnetic recording layer as well as the layer strength and adhesion of the magnetic recording layer. Furthermore, the core material of the recording and reproducing heads must have a sufficiently high saturation magnetization to enable the recording of data onto a magnetic recording medium having a high coercive force.
Magnetic materials such as Permalloy and Sendust have been used as a recording and reproducing head core material having a high saturation magnetic flux density. However, these magnetic metals have poor high frequency characteristics due to their small specific resistance and can be used only when formed into multi-layered cores. Furthermore, very thin layers of the magnetic materials must be fabricated for magnetic recording and reproducing heads requiring a high frequency response. The use of such multi-layered thin layered core materials is very disadvantageous from the manufacturing standpoint.
At present, for magnetic recording and reproducing heads having a frequency response as high as 5 MHz or so, a ferrite material (e.g.-nickel-zinc ferrite, or manganese-zinc ferrite) are used. However, the saturation magnetization of such ferrites is as high as 4000 Gausses and the coercive force of a recording medium which can be used with a magnetic recording head using such ferrites is limited to recording mediums having a coercive force at or below 700 Oe.
As noted above, in conventional magnetic recording systems using longitudinal magnatization of the recording medium, it is difficult to realize a high density magnetic recording device having high frequency recording capability due to the technological problems of manufacturing a recording medium which reduces the influence of demagnetization due to the residual magnetization and the problems of fabricating recording and reproducing cores suitable for such a recording medium.
In order to solve some of the above-noted problems, the present inventors have developed a perpendicular recording system, (hereinafter referred to as a perpendicularly magnetized recording system), using a single pole magnetic head in conjunction with a magnetic layer having a easy axis of magnatization perpendicular to the medium plane. This system was described on pages 184 and 187 of the Text of National Convention of Electronic and Communication Society of Japan, 1976 and disclosed in Japanese patent application Numbers 51-51574 and 51-106506, respectively laid open on Nov. 11, 1977 under unexamined publication number 134,706/77 and Mar. 25, 1978 under unexamined publication number 32,009/78.